Bright dip



Patented Aug. 14, 1945 BRIGHT DIP Harry Robert Dittmar, Wilmington, Del., aslignor to E. I. du Pont de Nemours a Company, Wilmington, Del, a corporation of Delaware No Drawing. Application April 10, 1942, Serial No. 438.457

7 Claims.

This invention relates to a process for the cleaning of metals and more particularly to bright dipping copper and copper-containing alloys during their finishing treatment.

Heretofore it has been customary in the treatment of copper, brass, and other alloys containing a high percentage of copper, and particularly those carrying oxide scale produced during brazing or hard soldering, to pickle the finished product in acid such as sulfuric acid, nitric acid, hydrochloric acid, or mixtures thereof, some of which mixtures may contain dichromates and other coloring agents, in order to bring out a final high luster on the product. Metals so treated. however, often tarnish rapidly after contact with air and as a result the initial desirable appearance is lost before the product reaches the ultimate consumer.

An object of the present invention is to provide an improved process for the bright dipping of copper and copper-containing alloys. Another object is to provide a bright dipping bath wherein rods, tubes, and fabricated parts of copper, brass, and similar metal alloys high in copper may be treated whereby a high surface luster is obtained which is retained for a considerable period of time. Yet another object is to provide a glycolic acid bath for the bright dipping or copper and brass. Other objects and advantages of the invention will hereinafter appear.

.The above and other objectsmay be accom-'- plished by employing a glycolic acid bath for the treatment of copper, brass, bronze, and other alloys of high copper content (i. e., 40% copper or better) subsequent to their fabrication. Such a bath may contain from 0.25 to 50% of glycolic acid with in the order of from 1.0 to 5.0% of the lycolic acid as the preferred concentration. The

bath may be used not or cold although it effect is more rapid with a heated solution; Moreover, it has the outstanding advantage in contradistinc tion to the strong acid baths heretofore used in bright dipping in that even when hot it does not give oil suflocating vapors which render the use of the strong acid baths not only restricted to locations where excellent ventilation is provided but also restricted because of the physiological eflects.

Ordinarily a lycolic acid bath, either hot or cold. is suitable for the treatment of metals subiect to normal discoloration but if the article is coated with a deep scale it is often desirable to employ an electrolytic bath-with glycolic acid as the electrolyte. Baths of this nature are especially effective if during the brightening operation the parts being brightened are alternately made the anode and the cathode by reversal of the polarity of the electrical current,

Glycolic acid baths are especially eflective in preserving a bright color on the metal surface. This use is illustrated by the treatment of copper or brass rods, tubes, fabricated articles, and the like which are first dipped in a strong acid bath, such as one containing 8 ozJgal. sulfuric acid and 1.5 oz./gal. sodium chromate solution, to remove tarnish and heavy scale. Subsequent to washing the part from such acid treatment it is dipped into a 2% hot aqueous glycolic acid solution, removed from the bath, and the solution remaining on the part allowed to dry. or if desired, I

Glycolic acid, while it is an eii'ective agent for the bright dipping of the aforesaid metals, may also be used with other materials such as tartaric acid, calcium acid phosphate and the like. Furthermore, while glycolic acid is adaptable as a bright dipping medium and tarnish removin material even at fairly low concentrations, in applications wherein it is desired to restrict surface etching to the minimum amount salts, and more particularly the alkali metal and alkaline earth metal salts of glycolic acid. and particularly the sodium and potassium salts thereof, may be employed. In these instances the cleaning appears to be eflected by the glycolat ion in solution.

I claim:

l. A process for preserving the color of high copper-containing metals which comprises dipping a metal containing at least 40% copper into an aqueous glycolic acid bath.

2. A. process for preserving the color of high copper-containing metals which comprises dipping a metal containing at least 40% copper into acid bath containing from 1.0 to 5.0% giycolic acid at a temperature between 100 and 212 1".

5. A process for preserving the color or brass parts which comprises dipping bright colored tabricated parts of brass into an aqueous glycclic acid bath containing from 1.0 to 5.0% glycolic acid at a temperature between 100 and 212 F.

6. In a process for preserving the color 01' febricated brass parts which comprises bright dipping manufactured parts fabricated of brass 10 colic acid.

and thereafter preserving the bright color there- HARRY nonsm" 0m. 

